Method for cleaning a formation in the vicinity of a well bore



37"512 XH 'vL'PUaZl March 15, 1966 G D, ORTLOFF 3,240,271

METHOD Foa CLEANING A FORMATION 1N THE vzcwmf op A WELL BORE- *oiginal Filed sept. 12, 195e Gerold D. Orloff lnvenor f E Byfw'f?. Attorney hay) 20 Claims. (Ci. 156-9) This application is a continuation of copending application .Serial No. 609,497, filed on the 12th day of September, i956, now abandoned.

The present invention is broadly concerned with an improved method for cleaning up tin injection weil bore hole. The invention is directed toward a method for increasing the susceptibility of the area about the well to accept the introduction ol injected rluids.

lne specific atinpttition of the present invention is concerned with an improved method for the recovery of crude petroleum oil from subterranean formations wherein an improved technique for carrying out a secondary' recovery operation is utilized, in accordance with the specific adaptation of the process, the area adjacent and about an injection bore hole is specially treated with carbon dioxide in a manner to render more effective a second stage step wherein an oil scavenging huid such as water is injected into the injection hole and caused to flow to ward one or more production wells.

lt is known in :he art that after e reservoir has been subjected to secondary recovery operations such as water- 'tlooding the arca about the injection well bore holes tends to become relatively non-susceptive to the further introduction oi fluids. This is due to the fact that the pores oi the formation tend to he cio-"ged with mud, scale such t A various methods and techniques for removing oil in secondary recovery operations. For example it has been suggested that gas be injected and that the reservoir be repressured. Furthermore it is known in the art to inject water at an injection well and to cause this water to flow toward a producing well driving oil ahead of it to the producing well. Another procedure suggested has been vto introduce a bank of low-boiling hydrocarbon such as propane and to drive this bank by means of either water or natural gas toward the producing well= These methods have been successful to some degree. However, in many instances, the beneficial results have not been significant. i

As pointed out heretofore in oil production processes, the arca about a bore hole becomes less porous due to seule and mud clogging. Thus, it a conventional technique such as water flooding or propane washing be employed. it is often difficult to inject these :fluids effectively and etliciently in't'ia formation. A considerable and high-pressure drop isericountered in the area about the bore hole.

ln accordtince with the present invention,icarbon dioxide under a very high pressure is injected into the bore hole and the bore hole then sealed off. A time period is allowed to elapse :it the end of which the pressure is released. During the time that pressure is maintained on the bore hole, the carbon dioxide sceps into and dissolves iu the residual luids for several ice about the circumference of the bore hole. When the pressure is released on the carbon carbon dioxide, the carbon dioxide expands and exerts a gus pressure on the residual oil and other tluids causing them to backow into the from the pores thereby producing a highly'porous formation about the bore hole. ln addition, the removal ot' the residual oil secured by this process increases the susceptibility of the area about the bore hole for further liquid injection. During the backllowing operation, the liquid or tluid is pumped from the injection well. Water or any other suitable oil-displacing fluid is then pumped into the formation through the injection well and caused to ow toward the production wells.

The process of the present invention may be fully understood by reference to the drawing illustrating one embodiment of the same. Referring speciiically to the drawing, an oil-containing formation 1 is shown positioned below the earths surface 2. Bore holes 3, 4, and S extend from the earths surface into the oil-containing formation. Suitable ports or conduits 6, 7, and 8 permit tluid to ow between the formation 1 and well bore holes 3, 4, and 5 respectively.

ln accordance with the present invention, carbon dioxide is introduced under pressure and by suitable means through bore hole 4 and the bore hole then sealed olf. .A period of time is then permitted to lapse during which the carbon dioxide seeps into and dissolves in the residual oil and other tluio's about the bore hole in area. A. Thereafter pressure is released on the bore hole 4 and residual oil baclttlows into bore hole 4 and is removed by suitable pumps. This backowing causes scale, mud parrieles. and the like to be removed from the pores of the formation about the bore hole.

Upon completion of this phase of the operation, a flooding medium such as water, a bank of propane. gas, or the like. is introduced by suitable means through core hole 4. This llooding medium is caused to tlow through the formation in the direction of bore holes 3 and 5 and is removed along with the recovered oil by means ot' these bore holes to the surface.

The present invention is concerned with :tn eilective method for cleaning up a well bore hole immediately about the bore hole. A specific adaptation of the invention in essence comprises a particlulzir arrangement of processing secondary recovery steps. The process consists initially in the step of injecting a limited quantity of carbon dioxide into an injection bore hole. The quantity should be at least enough to penetrate at least 3 to 4 feet from the bore hole. The hole is then sealed ot at an elevated pressure which is in the range from about 1,000 to 12,000 pounds per square inch but less than the pressure required to lift the overburden. A preferred pressure is in the range from about 1,000 to 2,000 pounds per square inch. The hole is sealed oil for zi period of time which is in the range from about one to twelve hours. The pressure and time used will depend upon the type of oil formation being treated. Upon release of the pres-- sure from the injection well, pumping is continued as long as the backllow of fluids continues. After this stage water or other driving medium is introduced in a conventional manner. The operation is very desirable in that the injected uid such as water can fan out on a much greater periphery, namely the circumference of the purged area rather than the circumference of bore hole 4.

What is claimed is:

1. Improved method for the recovery of oil from a silbterranetin formation in a secondary recovery operation which comprises the steps of injecting a treating ugent consisting essentially ot' carbon dioxide into an injection well', sealing olf the injection well for zi period of time :it a pressure in excess ol the formation pressure such thzit the carbon dioxide will he forced several l'cct into the formation; releasing the pressure in said injection well at the cnd of said period of time; whereby fluid from the formation backflows into said injection we l; removing said fluid from said injection well and thereafter introducing a flooded fluid into said formation about said ini tion weil and causing said flooding fluid to flow to a producing well.

2. Process as dened in claim i wherein said time period is ir. the range from about oi twelve hours. Process as deduco' in claim i in wnich the treating yget is injected in a niantity sutii into ,he formation a distance of at least about 3 to 4 feet rom the injection well.

si. An improved method for the recovery of oil from subterranean formation in a secondary recovery operaion comprising injecting a treating agent consisting esseniaily of carbon dioxide into an injection well; maintaining the pressure of said carbon dioxide i thin the bore nole until the desired quantity of carbon dioxide has been forced into the formation: th reafter releasing the pressure in said injection weil whereby tiuid within said formation backflows into said injection well thus reducing the oil saturation of the formation adjacent the injection welii-rmoving said fluid from said injection well and thereafter introducing a iioocii d fluid into said formation about said injectionweil and causing said flooding fluid to flow to a producing well.

5. A process as defined by claim i wherein the pressure maintained on said weil bore is in ine range from about 1,00@ to 12,00() lbs. per square ir ch.

A process as defined by claim d wherein the pressure main ained on said well bore is within the range of LOU() to 2,000 lbs. per square inch.

7. An improved -niethod for increasing the injectivity of an injectionweli drilled into a subterranean formation whichcomprises the steps o: injecting a treating agent consistingl essentially of carbon dioxide into an linjection well n. p' rsure in he't'ormation pressure in a gunrititj sun cient to penetrate several feet into the formation; ser., .g ot the injection neil for a period of time'. releasing the pressure in sain "jection weil at the end of said period of time; remo ing said fluid from said injection well.

8. An improved method for increasing the injectivity of ari injection well drilled into a subterranean formation which comprises the steps of: injecting a treating agent consisting essentie. ly of carbon dioxide into said injection well under pressure in excess of the formation pressure until carbon dioxide has been forced several feet into the formation; thereafter releasing the pressure in said injection weil whereby carbon dioxide injected into the formation expands thus driving fluid from within the formation back into said injection well thus reducing oil saturation of the formation adjacent the injection well; and removing said fluid from said injection well.

9. A method for increasing the injectivity of an injection well drilled into :1 subterranean formationco taining petroleum which comprises the steps of: injecting carbon dioxide into said injection well at a pressure sufficient to permit saidcarbon dioxide to penetrate several feet into the formation: sealing ofi the injection well for a period of time; releasing the pressure in said injection well at. the end of said period ofy time; and

l removing fluid from said injection well.

l0. Process as defined in claim 9 wherein said period lof time is in the range from about one to twelve hours.

Gon the water and carbon dioxide water and carbon dioxide from the well.

of the formation pressure until carbon dioxide has been forced at least several fe-:t into the formation; and thereafter releasing the pressure in said injection Well whereby carbon dioxide injected into the foririiition expands thus driving fluid from the formation back into said injection well thus reducing oil saturation of the formation adjacent the injection well and removing plugging meteuai from the face of the well bore adjacent the formation.

.et method of increasing the transfer of an oil recovery fluid from an injection well which contains water into the surrounding oil bearing formation in which the wel] has been formed and wherein a relatively fluid impcrvious slain has been deposited on the surface of Said oil bearing formation. which comprises introducing under pressure carbon dioxide adjacent to said fluid impervious slcin said carbon dioxide used being at least 20 pounds per foot of vertical thickness of said oil bearing formation, continuing the injection of carbon-dioxide to mainA tain the pressure until said skin has been destroyed and thereafter injecting an oil recovery 'duid into the well.

i3. in the method of claim 12 said carbon dioxide. being injected at a pressure in excess of 100 p.s.i.

i4. ln the method of claim 12, the additional step of back flowing the well' by suddenly reducing the pressure on the carbon dioxide.

15. in the method of claim i2. the additional step of back flowing the well by suddenly reducing the pressure on the carbon dioxide and withdrawing the carbon dioxide and water from the well.

i6. A method of increasing the transfer of an oil recovery fluid from an injection weil into the surrounding oil bearing formation in which the well has been formed and wherein a relatively fluid impervious skin has been deposited on the surface of said oil hearing formation, which comprises introducing under pressure water and carbon dioxide adjacent to said fluid impervious skin said carbon dioxide used being at least 2l) pounds per foot of vertical thickness of said oil bearing formation7 continuing the injection of water and carbon dioxide to maintain the pressure until said skin has been destroyed and thereafter injecting an oil recovery fluid into the well.

. on the water and carbon dioxide.

19. in the method of claim i6. baci: flowing the well by suddenly the additional step of reducing the pressure and withdrawing the 20. A method of increasing the injectivity of an injcc tion well drilled into a subterranean formation which comprises: injecting carbon dioxide under pressure into the well; maintaining sufficient pressure on the well to permit the carbon dioxide to seep into the formation iinmediately adjacent thev well; thereafter releasing thc pressure in said well; removing fluid from said injection well; and then injecting an oil recovery fluid into the well.

References Cited by the Examiner UNTED STATES PATENTS 2,623,596 l2/l952 Whorton et al. `l66-7 2,811,209 lli/i957 Elkins 166-143 2,850,098 9/l958 Moll et al. 16o-Q43 CHARLES E. OCONNELL, Primary Examiner.

BENJAMN BENDETT, Examiner. 

7. AN IMPROVED METHOD FOR INCREASING THE INJECTIVITY OF AN INJECTION WELL DRILLED INTO A SUBTERRANEAN FORMATION WHICH COMPRISES THE STEPS OF: INJECTING A TREATING AGENT CONSISTING ESSENTIALLY OF CARBON DIOXIDE INTO AN INJECTION WELL AT A PRESSURE IN EXCESS OF THE FORMATION PRESSURE IN A QUANTITY SUFFICIENT TO PENETRATE SEVERAL FEET INTO THE FORMATION; SEALING OFF THE INJECTION WELL FOR A PERIOD OF TIME; RELEASING THE PRESSURE IN SAID INJECTION WELL AT THE END OF SAID PERIOD OF TIME; AND REMOVING SAID FLUID FROM SAID INJECTION WELL. 